The subject disclosure relates to a gradiometric parallel superconducting quantum interface device, and more specifically, to a gradiometric parallel superconducting quantum interface device that can be suitable for frequency tuning of superconducting quantum bits.
Many different types of superconducting devices regard superconducting quantum interference device (“SQUID”) technology. The critical current of a SQUID can be tuned by applying a magnetic flux to the loop of the SQUID. The relation between magnetic flux and the critical current is of great importance in several applications such as, in magnetometers and in frequency tuning of superconducting microwave devices (e.g., resonators and quantum bits).
The very high sensitivity to magnetic flux can also be a disadvantage for qubit applications since fluctuations can lead to qubit dephasing. By utilizing a gradiometric design, fluctuations in the absolute global magnetic field can be eliminated and only fluctuations in the magnetic field gradient will lead to dephasing. Conventional gradiometric SQUID design comprises twisting a direct current (“DC”) SQUID loop such that the loop crosses over itself and thereby creates two loops and two magnetic fluxes. Typically, to separate the electrodes a dielectric material is deposited at the crossover location in the gradiometric design. However, said positioning of the dielectric material can negatively affect the performance of superconducting quantum bits; thereby limiting the applications of conventional gradiometric SQUIDs.